Nitrogen over-enrichment

Paerl, H.W., Dennis, R.L., and Whitall, D.R. (2002) Atmospheric deposition of nitrogen implications for nutrient over-enrichment of coastal waters. Estuaries 25, 677-693. 

Paerl, H. W., and Fogel, M. L. (1994). Isotopic characterization of atmospheric nitrogen inputs as sources of enhanced primary production in coastal Atlantic Ocean waters. Mar. Biol. 119, 635—645. Paerl, H. W., Dennis, R. L., and Whitah, D. R. (2002). Atmospheric deposition of nitrogen Implications for nutrient over-enrichment of coastal waters. Estuaries 25, 677—693. 

Notwithstanding unequivocal benefits associated with the acceleration of the global N cycle in terms of satisfying societal demands for food and fuel, the negative environmental consequences to estuaries and coastal seas caused by over-enrichment of nitrogen are significant (Howarth and Marino, 2006 Rabalais, 2002). For example, two-thirds of the coastal rivers and bays in the United States are moderately to severely... 

Rotational-echo double-resonance (REDOR)(75,79) is a new solid-state NMR technique which is sensitive to through-space carbon-nitrogen interactions between selectively 13C and 15N-enriched sites separated by up to 5A (20-22). The parameter directly measured in a REDOR experiment is the heteronuclear dipolar coupling constant DCN, which is in itself proportional to the inverse third power of the intemuclear distance, rCN. It is this dependence on (icn)3 which accounts both for REDOR s ability to accurately measure short distances and its insensitivity to longer-range interactions. As a technique which can probe, in detail, intermolecular interactions over a distance range of 5A, REDOR is well suited to studying the distribution of small selectively-labeled molecules in polymer delivery systems. 

Experiments with mono- N-labeled amidines (the label is equally scrambled over both nitrogen atoms) have shown that in the 2-R-5-nitropyrimidines the excess of the enrichment is lower than that in the amidine (see Table III.2) (86JOC71). These measurements clearly indicate that during the reaction some labeling is lost. This result leads to the conclusion that besides formation of a mono- N-labeled 2-phenyl-5-nitropyrimidine (108), in which the N-label is scrambled over both nitrogens, a mono- N-labeled 2-phenyl-5-nitropyrimidine (109) is also obtained in which only one nitrogen is N-labeled (the benzamidine acts in this reaction as N-C donor) (Scheme III.55). 

Iron was chosen as the reference element because its major source is likely to be soil and it is measured with good accuracy and precision by FIXE. Crustal abundances were taken from Mason (21). Enrichment factors greater than 1 indicate an enrichment of that element relative to crustal abundances values less than 1 indicate a depletion. The results of this calculation are shown in Table 4. For this calculation it was assumed that ammonium and nitrate accounted for all aerosol nitrogen. It is seen that Si and Ca are near their crustal abundance, indicating a probable soil dust source. The low EF for Al is probably due to a systematic error in the Al measurement rather than a true depletion. Potassium, although present in small concentrations, is slightly enriched relative to crust. The other fine aerosol species, C, N, S, and Pb are enriched by factors of thousands over their natural crustal abundance, indicating that they are not due to wind-blown dust. 

When a second nitrogen atom is introduced into the pyridine ring the basicity is reduced (pjRTa 5.23 for pyridine and 2.33 for pyridazine). The effect of the additional substituents on pKK depends on the position of the substituents (Table 3). An extensive set of pK values of pyridazine derivatives has been submitted to correlation analysis using the Hammett and the two Taft equations, which shows that the pKa values are most sensitive to the effect of a 2-substituent followed by the effects of 3- and 4-substituents. The interactions between nitrogen atom and 2-substituents represent over 70% of the inductive character. The composition of the effects of +M 4-substituents is significantly enriched in the resonance interactions, whereas -M 4-substituents interact with the nitrogen atom mainly by induction (77MI21201). 

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